Metal casting process using destructible pattern



6 G. s. MOXLOW ETAL I I 3,

METAL CASTING PROCESS USING DESTRUCTIBLE PATTERN Filed March 20, 1964GENESATOR CONTRQLS Al R SOLVENT FIG. 4

INVENTORS GEORGE S. MOXLOW 8\ I U f-l4 BY ADHEMAR O. DEWITTE FIG. 5

ATTORNEY United States Patent This invention pertains to a metal castingprocess and apparatus therefor and more particularly to improvements ina process in which an expendable plastic pattern is used as a form toproduce a mold cavity, the plastic pattern being removed prior to metalpouring by the application of heated vapor and/ or gases to the patternso as to produce a degradationand decomposition of the plastic materialat a temperature below the materials combustion ternperature, and toefiiect its decomposition within the mold whereby a mold cavity isformed.

,The invention involves aprocesstbr the casting of metal and theapparatus utilized in such process. The process comp-rises a few basicsteps. The firstof these is the embedding of a plastic pattern in thesand of a mold box, flask or drag substantially according toconventional practice. The plastic material from which patterns arecurrently being made and for which the process of this invention wasparticularly designed is the foamed or expanded polystyrene, athermoplastic material which begins to distort, degrade, soften and meltat about 175 F. Upon subjection to higher temperatures, degradation anddecomposition are accelerated, so that when heated vapors and/or gasesare introduced to the foamed polystyrene pattern relatively large massescan be decomposed and melted in a few minutes.

In some casting processes, particularly the cavityless mold process,molten metal is poured directly into a mold box containing the foamedpolystyrene pattern. Such processing generates intense smoke throughoutthe foundry area, fills the foundry with relatively toxic or norcousirritating fumes, and causes the operator to lose sight of the ingate sothe metal is sometimes poured on the foundry floor, resulting in poorcastings due to intermittent pouring. Breathing the irritating odors andsmoke issuing from burned polystyrene patterns causes labor complaints.In View of such difiiculties in processing, and since patterns of foamedpolystyrene are being provided in in-. creasing numbers by foundrycustomers and pattern makers, because of their lower cost in comparisonto conventional wood patterns, the inventive processing and apparatusdisclosed and described herein was created to resolve such problems.

The invention invloves forming a cavity in a mold box, flask or dragrammed with sand about anexpanded or foamed plastic pattern byintroducing .to the pattern while in the mold box a continuous flow, ofheated vapor and/ or gases at a temperature or temperaturessubstantially above the decomposition temperature ,of the plasticmaterial forming the pattern, until the plastic material has been meltedand a cavity formed in the mold box which is substantially thecomplement of the pattern. During their application to the plasticmaterial, the heated vapor and/ or gases are maintained at a temperatureor temperatures within a range of from somewhat above the temperature atwhich distortion of the plastic material occurs byheating along and thetemperature at which burning or combustion of the plastic materialefiected. Within such range of temperatures, degradation anddecomposition occur without appreciable smoke or furnes and when theplastic material is subjected to heated vapor and/ or gases at elevatedtemperatures of the range, decomposition is accelerated. To furtherincrease the rate and relative uniformity of pattern decomposition,where the pattern embodies sections of substantial thickness anddisproportion when compared to other major sections of the pattern, theinventive process provides for boring or otherwise forming holes in thethicker sections longitudinally thereof so that the heated vapors and/or gases will find their way into all major sections of the pattern atabout the same time, and decomposition will proceed in all such sectionspenetrated at a relatively uniform rate. A marked advantage of such heatand vapor distribution is that one surface section of the mold sand willnot become overcured by heat in comparison to mold sand surfaces exposedto such heat for a shorter period of time at the end of the patterndecomposition step.

A principal object of the invention is to provide a cavity mold for thecasting of metal, the cavity being formed upon the degradation anddecomposition of a plastic pattern embedded in the mold box by theapplication of heated vapors and/or gases to the plastic patternmaterial. Another object is the provision in such process of theapplication of heated vapors and/ or gases at a temperature ortemperatures below the temperature at which the plastic material iscombustible and above a temperature at which the material will notdistort upon heating alone. A further object is to degrade and decomposethe plastic material, whereby to form a cavity mold, without thegeneration of noxious fumes, gases and smoke.

Various further and more specific objects, features and advantages ofthe invention will appear from the descriptiongiven below, taken inconnection with the accompanying drawing, illustrating by way of examplea preferred form and embodiment of the invention.

, Reference is now made .to the drawing annexed hereto,

' forming an integral part of this specification and in which FIGURE 1is a perspective view of a mold box containing a plastic patternembedded in sand and having an upper surface exposed to View.

FIGURE 2 is a vertical sectional view taken substantially on the line2-2 of FIGURE 1.

, FIGURE 3 is a vertical sectional view, similar to FIG- URE 2, showingthe cope in place upon the mold box. FIGURE 4 is another verticalsectional View showing the apparatus, principally in diagrammaticoutline, for applying heated vapors and/or gases to the plastic patternin the mold box. i

FIGURE 5 is a vertical sectional view of the mold box and cope showingthe cavity formed in the mold box prior to introduction of molten metal.

It is to be understood that the form and configuration of the plasticpattern illustrated and described in this specification was selectedsimply for the purpose of illus-' trating a representative embodiment ofa structure upon which the process and apparatus herein disclosed canoperate. The pattern configuration is not of any particular significanceexcept insofar as it contains recesses and bosses to indicate that arelatively complex pattern form as well as a more simple, configurationcan be used in connection with the inventive process herein disclosed.

As shown in the several views of the drawing, the plastic pattern 10 isembedded in mold sand 12 contained within the mold box 14. Inconventional practice, the pattern-10 is placed on a plate (not shown)in a manner such that its internal recesses, if any, are exposedupwardly for filling with sand from above. Then the mold box is coveredwith a plate 16 and inverted so that the pattern 10 is exposed at thetop of the mold.

The plastic material of which many such patterns, in any desiredconfiguration, are currently made and upon which the invention has beenpracticed is a foamed or expanded polystyrene, a thermoplastic materialof lighta) weight-low density and low thermal conductivity. One

such material is that produced by the Dow Chemical Company of Midland,Michigan, under the trademark Styrofoam. The material tends to melt awayfrom a source of heat, but it does have a flash ignition temperature atslightly under 700 F., the self-ignition temperature being slightlyunder 800 F.

Other materials to which applicants believe the invention would lenditself without modification include the expanded polyethylene and theexpanded polyurethane materials. The foamed or expanded polyethyleneperforms substantially as do the polystyrenes when subjected to heatitmelts away to create a void around such heat sources, but burning is notinitiated except with an open flame and in the presence of oxygen. Inthe case of the polyurethane foamed material, it is relatively stable toabout 250 F., some swelling taking place from about 250 F. to 300 F.,and above 300 F. shrinkage and polymer degradation result.

After the pattern has been properly embedded in the mold sand, a cope 18filled with sand 20 is placed above the mold box 14. The cope sand isarranged with an ingate opening 22 to one or more areas of the patternand a riser opening 24 at one or more areas of the pattern. The copesand is packed closely about and upon the pattern 10 so that the contactplanes of sand and pattern in the mold box and cope will define thepattern after it has been removed and the mold cavity formed.

Some pattern configurations lend themselves to embedding only in a moldbox, the sand being rammed and packed about the pattern on all sides. Insuch case, the ingate opening and the riser opening or openings areformed directly in the mold box sand.

Where the pattern 10 is of such configuration that its degradation anddecomposition or melting under the application of heat will proceed withappreciable speed and relative uniformity throughout the pattern, orwhere the pattern sections are relatively thin, the pattern is embeddedwithout perforation. However, where pattern section thickness orthicknesses are appreciable, or the pattern is relatively large andmassive, or because of the patterns mass it would require a substantialperiod of time under the application of heated vapors and/or gases todegrade, decompose or melt, so that the mold sand would be unfavorablyaffected and a poor quality casting result, then under suchcircumstances the process of this invention calls for perforation of thepattern at and through sections thereof to provide passageways 26 fromthe ingate opening 22 to the several sections of the pattern, preferablyinterconnected together unless otherwise indicated, in order that athrough-flow of heated vapor and/r gases can be passed through theseveral passageways 26 in sections of the pattern to the riser opening24. Such a flue system in the pattern provides a relatively uniformdistribution of heat to the pattern sections with a resultant relativelyuniform degradation, decomposition and melting of the pattern.

Perforation of the pattern, of course, is done before the pattern isembedded in the mold sand. A conventional drill or other suitableperforating tools can be used. In order to prevent mold sand fromentering the passageways 26, their ends are plugged with polystyreneplugs 30, the ingate perforation 26a and riser perforation 261) beingcapped so that the caps can be easily removed after the ingate opening22 and riser opening 24 have been formed in the cope sand 20 packedclosely upon the pattern. The passageways 26 may be disposed in anydirection, but their location, direction and attitude should preferablybe such that they afford the greatest and most uniform distribution ofheat to all sections and surfaces of the pattern, whereby the patternwill degrade, decompose and melt at a relatively even rate throughout.

To effect such degradation and decomposition, the process of thisinvention provides for the application of heated vapor and/ or gases tothe pattern by way of the ingate opening 22, the riser opening 24, orboth such openings. The application of heat is provided by a generatorand control unit designated generally by the reference numeral 32, aconduit 34 leading from the unit, and a plurality of conduits 36 for theadmission of air, combustible gas and solvent to the unit 32. Thegenerator comprises generally a burner unit in which a mixture of gasand air is formed and ignited to produce a gas combustion at an elevatedtemperature. The generator can also include a heater for plastic solventwith or without air, and a device for blowing or otherwise causing thesolvent, now in vapor form and at an elevated temperature, to bedirected under pressure through conduit 34 to the pattern 10. The heatedair-gas mixture is also forced under pressure to the pattern whereby thelatter is rapidly suffused internally with heated gas or, when asolvent'is used, with a heated vapor. If a gas-air mixture is used, theplastic pattern distorts, degrades and melts; and if a heated solventvapor is employed, the pattern material distorts, degrades anddecomposes. Although heated gases issue from the riser opening 24, it isaccompanied by little if any solids in the form of a heavy dense smokesuch as issues when molten metal is poured directly to a plastic foamedpolystyrene pattern.

The temperature to which the heated vapor and/or gases are generated andapplied by the unit 32 fall within the range defined, at the lowerlimit, by the distortion or degradation temperature of the plasticmaterial upon heating alone and, at the upper limit, by its ignitiontemperature without flame. Since these materials vary widely in respectto such temperatures, because of density differences, compositionformulations, open or closed cell structures and other factors, theremay well be some variation and departure from the temperatures set forthin this specification. However, the primary function of the temperatureof the heated vapor and/or gases is the rate of degradation,decomposition and/or melting, and a relatively wide range of suchtemperatures is available and its limits for any plastic patternmaterial are easily and readily determinable.

Upon application of heated vapor and/or gases to the plastic pattern 10and its consequent destruction, the cavity 40, defined by the pattern10, is formed in the mold box 14, ready for acceptance of molten metalto form a casting which will be, in all material respects, substantiallya reproduction in configuration of the pattern. Upon completion of thedecomposition or melting of the plastic pattern 10, the generator andcontrol unit 32 and the output conduit 34 are removed from the mold foradmission thereto of the ladle or other vessel or device containing anddischarging molten metal to the mold box. When molten metal is pouredthrough the ingate opening 22, it will fill the cavity 40 and risethrough the riser opening 24, forming the desired casting. This castingstep is thus taken without the generation of plastic smoke or other suchemanation from the mold box.

The gases which can be utilized and combined by the generator unit 32include air and natural combustible gas, and oxygen and such gas.Solvents which can be heated to vaporization by the generator include,among others, methylene chloride, perchlorethylene, andtrichlorethylene. The controls for. such gases and vapors in theirheating and expulsion from the unit include onoif switches, in-limevalves, pressure valves, solenoid valves reponsive to the temperature ofthe vapors and/ or gases in the heating generator for admitting andclosing off such gases, or solvent from the generator, and whererequired or desired a blower unit for expelling the heated vapor and/orgases under pressure from the generator and through the output conduit34 to the pattern 10..

In essence, the process of this invention comprises the steps ofembedding a plastic pattern in sand in a mold box, covering such patternwith mold sand in a cope or in the mold box, providing an avenue ofentry through a combustible gas-air or gas-oxygen mixture, conduits,

passing solvent or solvent vapor, air or oxygen, and combustible gas tothe generator, controls for the generator comprising on-olf switches,in-line valves, solenoid valves, pressure valves, and optionally ablower unit to expel heated vapor and/ or gases from the generator underpressure.

Although a certain particular embodiment of the invention has beenspecifically disclosed herein for purposes of explanation, it will beapparent to those skilled in the art to which the invention pertainsthat additional embodiments and further modifications thereof, afterstudy of this specification, can be practiced or made. Reference shouldbe had to the appended claims in determining the scope of the invention.

We claim:

1. In a metal casting process,

embedding a pattern of expanded plastic material in the sand of a mold,providing at least one ingate opening and one riser opening in said moldleading to and from said pattern,

applying heated solvent vapor capable of degrading and decomposing saidmaterial to said pattern through one or more of said openings, degradingand decomposing said expanded plastic pattern in said mold to form acasting cavity therein substantially the complement of said pattern,pouring molten metal to said mold cavity to form a casting substantiallya reproduction of said pattern, said heated vapor being applied to saidpattern at a temperature below the combustion temperature of saidexpanded plastic material and above the temperature at which saidmaterial distorts under heating alone,

and prior to embedding said pattern in said sand perforating sections ofsaid pattern to provide passageways for conduction of said heatedsolvent vapor internally of said pattern, prior to embedding saidpattern in said mold sand.

2. The process defined in claim 1, including closing off the ends ofselected ones of said passageways against admission of mold sandthereinto.

3. Ina metal casting process,

embedding a pattern of expanded plastic material in the sand of a mold,providing at least one ingate opening and one riser opening in said moldleading to and from said pattern,

applying heated gases capable of degrading, decomposing and melting saidmaterial to said pattern through one or more of said openings,degrading, decomposing and melting said expanded plastic pattern in saidmold to form a casting cavity therein substantially the complement ofsaid pattern,

pouring molten metal into said mold cavity to form a castingsubstantially a reproduction of said pattern,

said heated gases being applied to said pattern at a temperature belowthe combustion temperature of said expanded plastic material and abovethe temperature at which said material distorts under heating alone, iand perforating sections of said pattern to provide passageways forconduction of said heated gases internally of said pattern, prior toembedding said pattern in said mold sand. 4. The process defined inclaim 3, including closing olf the ends of selected ones of saidpassageways against admission of mold sand thereinto. 5. In the processof making a casting mold having a mold cavity,

embedding a pattern made of plastic material in the sand of a mold,providing ports of ingress to and egress from said pattern in said mold,applying heated gases capable of degrading, decomposing and melting saidmaterial to said pattern through one or more of said ports,

said heated gases being applied at a temperature below the combustiontemperature of said plastic material and above the temperature at whichsaid plastic material distorts under heating alone, degrading,decomposing and melting said plastic pattern in said mold to form acasting cavity therein substantially the complement of said pattern,prior to embedding said pattern in said sand perforating sections ofsaid pattern to provide passageways therethrough for conduction of saidheated gases internally of said pattern, and closing off the ends ofselected ones of said passageways against admission of mold sandthereinto,

prior to embedding said pattern in said mold sand. 6. In the process ofmaking a casting mold having a mold cavity,

embedding a pattern of a material degradable, decomposable and meltableunder heat in the sand of a mold, providing ports of ingress to andegress from said pattern in said mold, applying heated gases capable ofdegrading, decomposing and melting said material to said pattern throughone or more of said ports,

said heated gases being applied at a temperature below the combustiontemperature of said pattern material and above the temperature at whichsaid pattern material distorts under heating alone, degrading,decomposing and melting said pattern material in said mold to form acasting cavity therein substantially the complement of said pattern,prior to embedding said pattern in said sand perforating sections ofsaid pattern to provide passageways therethrough for conduction of saidheated gases internally of said pattern, and closing off the ends ofselected ones of said passageways against admission of mold sandthereinto, prior to embedding said pattern in said mold sand.

References Cited by the Examiner UNITED STATES PATENTS MARCUS U. LYONS,Primary Examiner.

1. IN A METAL CASTING PROCESS, EMBEDDING A PATTERN OF EXPANDED PLASTIC MATERIAL IN THE SAND OF A MOLD, PROVIDING AT LEAST ONE INGATE OPENING AND ONE RISER OPENING IN SAID MOLD LEADING TO AND FROM SAID PATTERN, APPLYING HEATED SOLVENT VAPOR CAPABLE OF DEGRADING AND DECOMPOSING SAID MATERIAL TO SAID PATTERN THROUGH ONE OR MORE OF SAID OPENINGS, DEGRADING AND DECOMPOSING SAID EXPANDED PLASTIC PATTERN IN SAID MOLD TO FORM A CASTING CAVITY THEHREIN SUBSTANTIALLY THE COMPLEMENT OF SAID PATTERN, POURING MOLTEN METAL TO SAID MOLD CAVITY TO FORM A CASTING SUBSTANTIALLY A REPRODUCTION OF SAID PATTERN, 